Abstract
The rate of the intra-molecular redox decomposition of the tris(oxalato)cobaltate(III) ion [Co(Ox) 3] 3− is greatly accelerated by irradiation with visible light of aqueous acidic solutions containing the tris(2,2′-bipyridine)ruthenium(II) ion [Ru(bpy) 3] 2+. The rate of the light-induced reaction in hydrochloric acid with an acidity range 0.05–0.18 mol dm −3 is of zero-order with respect to the [Co(Ox) 3] 3− ion concentration and is proportional to the light-intensity irradiated and also essentially to the [Ru(bpy) 3] 2+ ion concentration. Moreover, the rate is independent not only of the oxalate ion concentrations, but also of the acidity over the range 0.05–0.18 mol dm −3 hydrochloric acid. The ionic-strength dependence, as well as temperature dependence, were extremely small. The [Ru(bpy) 3] 2+ concentration does not change during the occurrence of the reaction and the tris(2,2′-bipyridine)ruthenium(II) ion acts as a homogeneous catalyzer. However, a dramatic indication that the situation was rather different was found in the stronger acid solutions of 0.5 or 1.0 mol dm −3 hydrochloric acid, in which the [Ru(bpy) 3] 2+ concentration decreased greatly immediately after the initiation of reaction and then increased up to the initial concentration. Such a decrease at the initial stage of the reaction disappeared by addition of oxalate before the start of the reaction. A chain mechanism of reaction is proposed to account for these results.
Published Version
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